This invention relates to a writing instrument which generates signals representative of the force applied and the direction of motion taken in writing, and more particularly to improvements therein.
In a U.S. Pat. No. 3,145,367, there is described and claimed a pen which uses switches to generate signals when used in writing, which indicate the direction which is being written. A specific sequence of direction signls are used to sequence a specific one out of many magnetic core shift registers. The last stage or last magnetic core in the shift register, when actuated, indicates the character which has been written.
In an application for "Handwriting System", by Crane, et al., which is assigned to this assignee, filed Jan. 31, 1974, Ser. No. 438,413, (Attorney's Docket No. 73/341), there is described a pen which, instead of quadrantially placed switches for indicating direction of motion, uses quadrantially placed photodiodes, actuated by a light on the ink cartridge of the pen, to generate signals which are subsequently used for identifying the characters which have been written with the pen.
The use of photodiodes for generating pen motion signals is an improvement over the switches, in that switch contacts corrode or oxidize, or wear with use, which is a problem that does not affect the photodiodes. A pen with photodiodes for generating direction signals works effectively. However, if a pen signal generating system could be devised which not only provides direction signals but also can provide a signal indicative of the pen to paper force being used while writing, another dimension would be provided for enabling the accomplishment of character recognition from the output of a pen. One further problem that arises, is that the use of switches and photodiodes cause the pen to be somewhat bulky and therefore cumbersome to handle. If a system could be devised which could reduce the size and weight of the components used in the pen for generating signals, it would enable one to write more normally with the pen than is the case when the pen is cumbersome to hold and manipulate.